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Network foundations · Lesson 6 of 7

Follow a TCP connection

TCP helps two endpoints exchange an ordered stream of bytes. Following its connection setup makes it easier to distinguish reaching a service from securing the conversation.

SEE IT UNFOLD

Watch the TCP handshake

Follow the sequence, or move one step at a time.

Read all 4 steps
  1. Client asks to connect

    The client starts the usual TCP handshake. This is not an identity or encryption check.

  2. Server responds

    The server acknowledges the request and sends its own synchronization information.

  3. Client acknowledges

    The client acknowledges the server response. The exchange coordinates connection state and sequence numbers.

  4. Then application traffic

    The connection can carry application data. Acknowledged bytes do not prove that an application completed its job.

SEE THE IDEA

Three checks, three different answers

Compare the parts before making a security decision.

  1. TCP connection

    Can these endpoints establish a connection?

  2. TLS protection

    Can they establish protected transport with the required identity checks?

  3. Application result

    Did the requested action actually succeed?

A connection, protected transport, and a successful application action are different checks.
Read the visualWhat does a completed TCP handshake establish?

TCP coordinates a connection. Encryption, identity checks, and application results belong to other layers.

Establish the connection

In the usual three-way handshake, a client sends SYN, the server replies SYN-ACK, and the client responds ACK. This coordinates the connection state and sequence numbers.

Handle missing data

Sequence numbers and acknowledgments help TCP manage delivery. Missing data can be retransmitted. An acknowledgment concerns received bytes, not whether a business operation succeeded.

Keep security separate

TCP does not itself encrypt the stream or prove that a service is trustworthy. HTTPS commonly adds TLS over TCP; HTTP/3 uses QUIC instead, so not every web connection follows this diagram.

Put it in context

A fictional browser reaches a server’s TCP port, but certificate validation then fails. The completed TCP handshake shows a connection was established. It does not make the later identity warning safe to bypass.

A connection, protected transport, and a successful application action are different checks.

Read the sources

Make it stick.

Try one short question to check your understanding and save this lesson to your progress.

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